Active range-gated spectrometric standoff detection and characterization of bioaerosols

Abstract

In atmospheric sensing, one application that has demonstrated several impressive successes over the last two decades is LIght Detection And Ranging (LIDAR). With elastic signal returns, this technique remotely provides information such as the particle density and, for a multiple field of view LIDAR, the distribution in size of the aerosols as a function of the range along the probing laser beam. For this type of application, the return signal has the same spectrum than the laser source. Some specific techniques, such as Raman or resonant LIDARs, collect the return signal at wavelengths other than the source. However, these signals are usually narrow spectrally and are collected with a single bandpass spectral filter. Recently, the Canadian Defence Research and Development Branch has initiated the evaluation of a novel LIDAR concept which opens the possibility of collecting simultaneously the detailed spectral information contained in spectrally wide return signals. One drawback with this approach is the loss of simultaneous information at multiple ranges, i.e., the spectral information is available only for a specific range. Nevertheless, there are applications where the partial loss of range information is compensated by the gain resulting from the spectral information. This paper describes the concept and reviews the general model predicting the capability of this technique for the standoff detection of bioaerosols. It shows a numerical simulation of the anticipated spectral profiles collected with the proposed active range-gated fluorescent LIDAR for a particular bioaerosol as a function of ranges, and for both day and night operational scenarios.